A prior art fixing device used in copying machines and printers utilize a heat roller fixing method for fixing the toner image to a recording paper by passing the paper with the pre-fixed toner image through a pair of heated and pressurized rollers to melt the toner on the paper.
However, in a heat roller fixing method described above, a so-called offset phenomenon occurs where melted toner on the recording paper adheres to the roller, which had been a problem. Especially in a colored electrophotographic equipment, the releasing characteristics of the colored toners against the roller were not good compared to prior art black toners, and the occurrence of offset phenomenon was outstanding.
Therefore, in the present fixing device of electrophotographic equipment, especially in the colored electrophotographic equipment, it is indispensable to apply an offset preventing agent having small surface energy such as silicon oil to the surface of the roller in order to prevent offset phenomenon.
Next, a typical oil applying device for use in this type of fixing devices is explained. The oil applying device comprises an oil applying roller, oil applying felt, oil control blade, oil tank, and so on. The oil applying felt is positioned so that the upper end portion thereof contacts the oil applying roller, and the lower end portion thereof is submerged to the oil inside the oil tank. By the capillary action by the oil applying felt, the oil is carried up from the oil tank and applied to the surface of the oil applying roller. The oil applied to the surface of the oil applying roller is then wiped away of the extra oil by the oil control blade pressurized against the oil applying roller by a predetermined power to equalize the oil on the roller to a predetermined amount, and then the oil is further applied to the surface of a fixing roller at a contact portion B of the oil applying roller and the fixing roller.
As is disclosed in Japanese Utility Model Publication No. 59-37797, a thin leaf spring is typically used as a means for supporting said oil applying felt and pressurizing the same against the oil applying roller. The thin leaf spring is a leaf spring having a L-shaped cross-section made of stainless steel with a thickness of 0.2 mm, and it presses the oil applying felt to the oil applying roller along the longitudinal direction of the roller while being fixed to the oil tank by a fixing means.
However, in the above-mentioned method of pressing the oil applying felt onto the oil applying roller by use of a thin leaf spring, there were the following problems:
(1) the thin leaf film is apt to bend and twist during the manufacturing process, and it is difficult to hold the oil applying felt against the longitudinal direction of the oil applying roller in a uniform manner; and PA1 (2) the thin leaf film has small freedom in determining its design by the limitation from the size of its fixing portion and for holding the felt, so the spring constant could not be set to a small amount, leading to change in the contact status of the oil applying felt and the oil applying roller by assembly errors and change in thickness of the oil applying felt by abrasion.
As a result, oil is applied unevenly, causing problems such as offset, oil stain on the end of papers, and feeding errors of papers. On the other hand, the extra oil wiped away by the oil control blade will stay at the contacting portion (portion A in the drawing) of the oil control blade and the oil applying roller, but when the device is driven for a relatively long period of time by multiple-printing and the like, the oil which could no longer stay at the contacting portion overflows and contaminates the interior of the device.
The present invention aims at solving the above problems, and provides a fixing device having a uniform and stable oil applying function which prevents occurrence of uneven application and oil stains on papers.